A smooth starting method and system for V / F control of an electrically excited synchronous motor

Abstract

The application discloses a kind of smooth starting method and system of electrically excited synchronous motor V / F control, it is related to motor control technology, it is solved that open-loop control cannot position rotor initial position, resulting in asynchronous starting when starting, current fluctuation is big, prone to overcurrent problem, its technical scheme main points include: when electrically excited synchronous motor enters excitation stage, the three-phase induced electromotive force of stator is collected, and rotor initial angle is calculated;When electrically excited synchronous motor enters I / F control stage, the three-phase current and voltage of electrically excited synchronous motor are collected, and speed and torque current are adjusted by double closed loop control;When operating speed reaches the set switching speed, the voltage amplitude calculated and output by smooth function mathematical model is entered V / F control stage;The application observes rotor initial angle, so that motor smooth starting, improves the anti-step-out ability and stability of system by I / F double closed loop control, and constructs smooth function, smooth transition V / F control.

Description

TECHNICAL FIELD

[0001] The present application relates to motor control technology, more particularly, it relates to a smooth starting method and system for V / F control of an electrically excited synchronous motor. BACKGROUND

[0002] The conventional V / F control determines the steady-state output voltage of the frequency converter at different rotational speeds according to the V / F curve, so as to perform open-loop control on the synchronous motor. When the system is stably running, the motor stator current follows the change of the external load torque, and the active current and the reactive current are relatively stable. This control method has simple principle, small dependence on motor parameters, and low use cost, and is therefore widely applied. However, the open-loop control cannot locate the initial position of the rotor, thereby causing asynchronous starting during starting, large current fluctuation, and easy overcurrent. SUMMARY

[0003] The purpose of the present application is to provide a smooth starting method and system for V / F control of an electrically excited synchronous motor, which observes the initial angle of the rotor at the beginning of starting, so as to smoothly start the motor into the I / F control stage, improves the anti-step-out ability and stability of the system by constructing the I / F double closed-loop control, and constructs a smooth function to make the I / F control smoothly transit the V / F control, thereby solving the problems in the above background technology.

[0004] The above technical purpose of the present application is achieved by the following technical scheme: the method comprises:

[0005] S1. When the electrically excited synchronous motor enters the excitation stage, the three-phase induced electromotive force of the stator is collected, and the initial angle of the rotor is calculated through the three-phase induced electromotive force;

[0006] S2. When the electrically excited synchronous motor flux is established and enters the I / F control stage, the three-phase current and voltage of the electrically excited synchronous motor are collected, and the three-phase current and voltage are fed back to the target rotational speed through the inner loop active power control loop to adjust the rotational speed, and are fed back to the target torque current through the outer loop reactive power control loop to adjust the torque current;

[0007] S3. When the running rotational speed reaches the set switching rotational speed, the voltage amplitude calculated by the smooth function mathematical model is output, and the V / F control stage is entered.

[0008] Adopting the technical scheme, when the electrically excited synchronous motor enters an excitation stage, the initial angle of the motor rotor is solved through three-phase induced electromotive force of the electrically excited synchronous motor, so as to avoid asynchronous starting; when the excitation flux of the electrically excited synchronous motor is established, the motor is started stably to enter an I / F control stage, the active power and the reactive power are observed through three-phase current and other parameters of the electrically excited synchronous motor in the I / F control stage, the given target rotating speed and target torque current are adjusted in real time through the inner loop active power control loop and the outer loop reactive power control loop, so that the load capacity of the motor is greatly improved and the motor is not easy to lose step; with the increase of the rotating speed, after the motor operating speed reaches the set switching rotating speed, the output voltage amplitude generated by the I / F control is gradually and smoothly changed into the output voltage amplitude generated by the V / F control algorithm by using a smoothing function, so as to enter a V / F control stage and avoid large current impact caused by direct conversion from I / F to V / F.

[0009] Further, the step S1 comprises:

[0010] S11, three-phase induced electromotive force of the stator is collected, and after 3 / 2 conversion and coordinate conversion, M-axis voltage observation value and T-axis voltage observation value in the MT rotating coordinate system are obtained;

[0011] S12, the M-axis voltage observation value is integrated to obtain the stator flux linkage, the rotating speed is calculated through the stator flux linkage and the T-axis voltage observation value, and the initial angle of the rotor is obtained by integrating the rotating speed.

[0012] Further, in the step S2, the inner loop active power control loop comprises:

[0013] Three-phase current and three-phase voltage of the electrically excited synchronous motor are collected, the current and the voltage in the static two-phase coordinate system are obtained through 3 / 2 conversion, and the active power is calculated;

[0014] The high-frequency component of the active power is fed back to the target rotating speed, so as to adjust the rotating speed.

[0015] Further, in the step S2, the outer loop reactive power control loop comprises:

[0016] The difference between the reactive power observation value and the true value is calculated through the current in the static two-phase coordinate system, the q-axis inductance in the DQ rotor rotating coordinate system, the excitation flux linkage and the rotating speed adjusted by the inner loop active power control loop;

[0017] The difference is fed back to the target torque current after PI adjustment, so as to adjust the torque current.

[0018] Further, the step S3 comprises:

[0019] A switching time period is set, and during the switching time period, the voltage amplitude output in the V / F control stage is calculated by a smooth function mathematical model; after the switching time period, the voltage amplitude output in the V / F control stage is directly calculated.

[0020] The input of the smooth function mathematical model is the voltage amplitude output in the I / F control stage at the switching time, the voltage amplitude output in the V / F control stage at the current time, and the time.

[0021] Another aspect of the present application provides a smooth starting system for V / F control of an electrically excited synchronous motor, which comprises:

[0022] A rotor initial angle recognition module is configured to collect three-phase induced electromotive forces of a stator when the electrically excited synchronous motor enters an excitation stage, and calculate a rotor initial angle based on the three-phase induced electromotive forces.

[0023] An I / F double closed-loop control module is configured to collect three-phase currents and voltages of the electrically excited synchronous motor when the electrically excited synchronous motor enters an I / F control stage after the magnetic flux is established, and feed back the three-phase currents and voltages to a target rotating speed through an inner active power control loop to adjust the rotating speed, and feed back the three-phase currents and voltages to a target torque current through an outer reactive power control loop to adjust the torque current.

[0024] A V / F switching control module is configured to calculate the voltage amplitude output by a smooth function mathematical model when the rotating speed reaches a set switching rotating speed, and enter a V / F control stage.

[0025] Further, the rotor initial angle recognition module is configured to:

[0026] The three-phase induced electromotive forces of the stator are collected, and after 3 / 2 transformation and coordinate conversion, M-axis voltage observation values and T-axis voltage observation values in an MT rotating coordinate system are obtained.

[0027] The M-axis voltage observation values are integrated to obtain stator flux, and the rotating speed is calculated based on the stator flux and the T-axis voltage observation values, and the rotor initial angle is obtained by integrating the rotating speed.

[0028] Further, the inner active power control loop comprises:

[0029] The three-phase currents and three-phase voltages of the electrically excited synchronous motor are collected, the currents and voltages in a static two-phase coordinate system are obtained by 3 / 2 transformation, and the active power is calculated.

[0030] The high-frequency component of the active power is fed back to the target rotating speed, so as to adjust the rotating speed.

[0031] Further, the outer reactive power control loop comprises:

[0032] The difference between the reactive power observation value and the true value is calculated by the current in the static two-phase coordinate system, the q-axis inductance in the DQ rotor rotating coordinate system, the excitation flux linkage and the speed calculated after the active power control loop in the inner ring is adjusted;

[0033] The difference is fed back to the target torque current after PI adjustment, so as to adjust the torque current.

[0034] Further, the V / F switching control module is also used for:

[0035] A switching time period is set, the voltage amplitude output in the V / F control stage is calculated by a smooth function mathematical model in the switching time period, and the voltage amplitude output in the V / F control stage is directly calculated after the set switching time period;

[0036] The input of the smooth function mathematical model is the voltage amplitude output in the I / F control stage at the switching moment, the voltage amplitude output in the V / F control stage at the current moment and time.

[0037] Compared with the prior art, the present application has the following beneficial effects: the present application provides a smooth starting method and system for V / F control of an electrically excited synchronous motor:

[0038] 1. The I / F control algorithm is introduced to solve the problem of excessive starting current fluctuation under V / F control, so that the current during starting is proportional to the speed, and the current fluctuation is obviously reduced. Meanwhile, a rotor initial angle recognition module is designed in the excitation stage of the electrically excited synchronous motor before starting, so that the accurate rotor initial angle can be observed without a sensor, and the motor reverse rotation during I / F control starting is avoided.

[0039] 2. The collected motor three-phase current and voltage are fed back to the target speed and target torque current through the inner loop active power control loop and the outer loop reactive power control loop respectively, and finally the PI regulator is used to adjust the speed and torque current value of the given frequency converter, so as to improve the stability of the system, so that the output voltage of the frequency converter in the I / F control mode can match the external load in real time, and the output voltage size can be quickly responded and adjusted when the load suddenly changes, so as to prevent the motor from losing step.

[0040] 3. The smooth function mathematical model is constructed, so that when the running speed reaches the set switching speed, the I / F control is smoothly switched to the V / F control, during which the output motor stator voltage can be smoothly transitioned, and the large current impact and speed fluctuation caused by voltage step are avoided. BRIEF DESCRIPTION OF DRAWINGS

[0041] The drawings described herein are used to provide further understanding of the embodiments of the present application, constitute a part of the present application, and do not constitute a limitation on the embodiments of the present application. In the drawings:

[0042] Figure 1 A general V / F control schematic diagram provided for an embodiment of the present application;

[0043] Figure 2 A flowchart schematic diagram of a smooth starting method provided for an embodiment of the present application;

[0044] Figure 3 A rotor initial angle recognition module schematic diagram provided for an embodiment of the present application;

[0045] Figure 4 An I / F double closed loop control module schematic diagram provided for an embodiment of the present application;

[0046] Figure 5 A V / F switching control module schematic diagram provided for an embodiment of the present application;

[0047] Figure 6 A motor speed simulation data diagram provided for an embodiment of the present application;

[0048] Figure 7 A motor torque simulation data diagram provided for an embodiment of the present application;

[0049] Figure 8 A phase A stator current simulation data diagram provided for an embodiment of the present application. DETAILED DESCRIPTION

[0050] Hereinafter, the term "include" or "may include" used in various embodiments of the present application indicates the existence of the applied function, operation, or element, and does not limit one or more functions, operations, or elements to be added. Also, as used in various embodiments of the present application, the terms "include", "have", and their conjugates merely indicate the presence of the mentioned features, numbers, steps, operations, elements, components, or combinations thereof, and should not be construed as excluding the possibility of the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof.

[0051] In various embodiments of the present application, the expression "or" or "at least one of B or / and C" includes any combination of the listed terms or all combinations thereof. For example, the expression "B or C" or "at least one of B or / and C" can include B, can include C, or can include both B and C.

[0052] The terminology used in the various embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the various embodiments of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of the present application belong. The terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0053] For the purposes of the present application, the technical solutions and advantages will be further described in detail below with reference to the embodiments and drawings, the illustrative embodiments and the descriptions thereof are only used to explain the present application and do not limit the present application.

[0054] Referring to Figure 1 as shown, Figure 1 is a schematic diagram of a conventional V / F control, a target speed is given, a theoretical V / F curve is referred to, and the steady-state output voltage of the frequency converter SVPWM at different speeds is adjusted to open-loop control the synchronous motor. However, the open-loop control cannot locate the initial position of the rotor, thereby causing asynchronous starting during starting, large current fluctuation, and easy overcurrent.

[0055] Therefore, the present application provides a smooth starting method for V / F control of an electrically excited synchronous motor, which introduces I / F and V / F compound control containing rotor initial positioning during the starting stage to reduce current fluctuation during the starting stage.

[0056] Embodiment 1

[0057] The present embodiment provides a smooth starting method for V / F control of an electrically excited synchronous motor, referring to Figure 2 as shown, Figure 2 is a flowchart of the smooth starting method, and the method comprises the following steps:

[0058] S1, when the electrically excited synchronous motor enters the excitation stage, the three-phase induced electromotive force of the stator is collected, and the initial angle of the rotor is calculated through the three-phase induced electromotive force;

[0059] S2, when the electrically excited synchronous motor flux linkage is established and enters the I / F control stage, the three-phase current and voltage of the electrically excited synchronous motor are collected, and the active power control loop in the inner ring is fed back to the target speed to adjust the speed, and the reactive power control loop in the outer ring is fed back to the target torque current to adjust the torque current;

[0060] S3: When the running speed reaches the set switching speed, the output voltage amplitude is calculated through the smooth function mathematical model and the V / F control stage is entered.

[0061] Before the electrically excited synchronous motor starts, that is, when it enters the excitation stage, the initial rotor angle of the motor is determined by the three-phase induced electromotive force of the electrically excited synchronous motor. When the magnetic flux of the electrically excited synchronous motor is established, the motor starts smoothly and enters the I / F control stage. In the I / F control stage, the active power and reactive power are obtained by observing the three-phase current and other parameters of the electrically excited synchronous motor. The given target speed and target torque current are adjusted in real time through the inner active power control loop and the outer reactive power control loop, thereby changing the PWM waveform of the inverter SVPWM output voltage, ultimately significantly improving the motor load capacity and preventing it from losing steps. As the speed increases, after the motor operating speed reaches the set switching speed, a smoothing function is used to gradually and smoothly transform the output voltage amplitude generated by the I / F control to the output voltage amplitude generated by the V / F control algorithm, and then enter the V / F control stage, avoiding the large current shock caused by the direct conversion of I / F to V / F.

[0062] Step S1 includes:

[0063] S11, collecting the three-phase induced electromotive force of the stator, and obtaining the M-axis voltage observation value and the T-axis voltage observation value in the MT rotating coordinate system after 3 / 2 transformation and coordinate conversion;

[0064] S12. Integrate the M-axis voltage observation value to obtain the stator flux, calculate the speed using the stator flux and the T-axis voltage observation value, and integrate the speed to obtain the rotor initial angle.

[0065] Specifically, see Figure 3 As shown, Figure 3 This is a schematic diagram of the rotor initial angle recognition module. When the rotor of an electrically excited synchronous motor is electrically excited before starting, the excitation flux will induce a corresponding three-phase induced electromotive force U on the motor stator. a 、U b 、U c , the three-phase induced electromotive force is transformed by 3 / 2 to obtain U in the stationary two-phase coordinate system α 、U β , will U α 、U β After the coordinate conversion module VT is converted to the MT stator rotating coordinate system, the M-axis voltage observation value and the T-axis voltage observation value are obtained. The M-axis of the MT stator coordinate system always points to the stator flux and rotates synchronously with the stator flux. For ease of explanation, represents the M-axis voltage observation value, U M It represents the true value of the M-axis voltage, and the same applies to other symbols.

[0066] The principle of calculating the initial rotor angle is shown in the following formula:

[0067]

[0068] Where ψ is the stator flux, ω is the speed, It is the angle between the MT stator rotating coordinate system and the rotor coordinate system, also known as the load angle.

[0069] During the rotor excitation process, the stator generates an induced electromotive force U M =dψ / dt≠0, and the rotor is stationary, that is, U T =ωψ=0: Observed value at this time thereby Therefore, after integral processing Start to change until back Only then does the change stop, at which point the stator flux And the stator current is 0, so the angle between the MT coordinate system and the rotor coordinate system is It is the rotor initial angle θ0. Therefore, the entire rotor initial angle identification module can observe the rotor initial angle from the start of excitation to the completion of magnetic flux establishment.

[0070] When the magnetic flux of the electrically excited synchronous motor is established, the I / F control phase of step S2 is entered. In the I / F control phase:

[0071] The inner active power control loop includes: collecting the three-phase current and three-phase voltage of the electrically excited synchronous motor, obtaining the current and voltage in a stationary two-phase coordinate system through a 3 / 2 transformation, and calculating the active power; feeding back the high-frequency component of the active power to the target speed to adjust the speed.

[0072] The outer loop reactive power control loop includes: calculating the difference between the reactive power observation value and the true value through the current in the stationary two-phase coordinate system, the q-axis inductance in the DQ rotor rotating coordinate system, the excitation flux and the speed adjusted by the inner loop active power control loop; and feeding the difference back to the target torque current after PI adjustment, thereby adjusting the torque current.

[0073] Specifically, see Figure 4 As shown, Figure 4 This is a schematic diagram of the I / F dual closed-loop control module. The inner active power control loop is the speed regulation: the three-phase current I of the electrically excited synchronous motor is collected. a , I b , I c And the three-phase voltage value U a 、U b 、U c , through 3 / 2 transformation, we can get I in the stationary two-phase coordinate systemα , I β with U α 、U β , through I α , I β with U α 、U β Calculate the active power P. Speed ​​change component ω i The electromagnetic torque component generated is opposite to the torque direction, and the high frequency component HPF(P) of the active power is opposite to the speed change component ω i Therefore, HPF(P) is fed back to the target speed. To increase the torque damping characteristics of the system.

[0074] The outer loop reactive power control loop is torque current regulation: the current I in the static two-phase coordinate system is collected α , I β , q-axis inductance L in the DQ rotor rotating coordinate system q 、Excitation flux ψ m And the speed ω after adjustment by the inner ring i The above parameters are input into the reactive power observer to calculate the difference between the reactive power observation value and the true value ΔI T In the picture Directly given, respectively, are the M-axis and T-axis currents in the MT stator rotating coordinate system, of which the current that provides torque to the motor is the T-axis current, so the outer loop mainly adjusts The difference between the reactive power observation value and the true value ΔI T Feedback to T-axis current after PI regulation Real-time adjustment enhances the system's ability to adapt to load changes.

[0075] Step S3 includes:

[0076] Set the switching time period. During the switching time period, the voltage amplitude outputted by the V / F control stage is calculated by the smoothing function mathematical model. After the set switching time period, the voltage amplitude outputted by the V / F control stage is directly calculated.

[0077] The input of the smoothing function mathematical model is the voltage amplitude of the I / F control output at the switching moment, the voltage amplitude of the V / F control output at the current moment, and time.

[0078] Specifically, see Figure 5 As shown, Figure 5 The schematic diagram of the V / F switching control module is shown. The smooth function f(I / F, V / F, t) is constructed. When the running speed Reach the set switching speed ω switchWhen the frequency converter SVPWM output voltage amplitude starts to gradually switch from the amplitude output by the I / F control algorithm to the amplitude output by the V / F control algorithm, the large current impact and speed fluctuation caused by directly switching from I / F control to V / F control is avoided. The input of the smoothing function f(I / F, V / F, t) is the voltage amplitude output by the I / F control at the switching time, the voltage amplitude output by the V / F control at the current time, and the time. Within the set switching time period, the voltage amplitude output by the smoothing function is calculated, and after the switching time period, the voltage amplitude under the V / F control is directly output.

[0079] The smooth starting method of the V / F control of the electrically excited synchronous motor provided by the embodiment can locate the initial position of the rotor, avoid motor reverse rotation during I / F control starting, construct a smoothing function to automatically switch to V / F control after the running angular velocity reaches the set angular velocity, and minimize the influence of mode switching on the speed and current. The double closed-loop control of active power and reactive power is introduced in the I / F control to increase the load damping characteristics of the system, adjust the current vector amplitude in real time, greatly enhance the stability and dynamic characteristics of the system, and solve the step-out problem of the motor under I / F control.

[0080] The embodiment further provides a smooth starting system of V / F control of an electrically excited synchronous motor, which is used to implement the smooth starting method of V / F control of the electrically excited synchronous motor.

[0081] The rotor initial angle recognition module is used to collect three-phase induced electromotive forces of the stator when the electrically excited synchronous motor enters the excitation stage, and calculate the rotor initial angle through the three-phase induced electromotive forces.

[0082] The I / F double closed-loop control module is used to collect three-phase currents and voltages of the electrically excited synchronous motor when the electrically excited synchronous motor finishes the establishment of the magnetic chain and enters the I / F control stage, feed back to the target speed through the inner loop active power control loop to adjust the speed, and feed back to the target torque current through the outer loop reactive power control loop to adjust the torque current.

[0083] The V / F switching control module is used to calculate the output voltage amplitude through the smoothing function mathematical model when the running speed reaches the set switching speed, and enter the V / F control stage.

[0084] The rotor initial angle recognition module, referring to Figure 3 is used to

[0085] The three-phase induced electromotive forces of the stator are collected, and after 3 / 2 transformation and coordinate conversion, the M-axis voltage observation value and the T-axis voltage observation value under the MT rotating coordinate system are obtained.

[0086] The M-axis voltage observation value is integrated to obtain the stator flux, the speed is calculated using the stator flux and the T-axis voltage observation value, and the speed is integrated to obtain the rotor initial angle.

[0087] I / F dual closed-loop control module, see Figure 4 As shown, it includes an inner active power control loop and an outer reactive power control loop;

[0088] The inner active power control loop includes:

[0089] The three-phase current and three-phase voltage of the electrically excited synchronous motor are collected, and the current and voltage in the stationary two-phase coordinate system are obtained through 3 / 2 transformation, and the active power is calculated; the high-frequency component of the active power is fed back to the target speed to adjust the speed.

[0090] The outer reactive power control loop includes:

[0091] The difference between the observed reactive power value and the true value is calculated using the current in the stationary two-phase coordinate system, the q-axis inductance in the DQ rotor rotating coordinate system, the excitation flux, and the speed adjusted by the inner active power control loop; the difference is fed back to the target torque current after PI adjustment, thereby adjusting the torque current.

[0092] The V / F switching control module, see Figure 5 As shown, it is used for:

[0093] Set the switching time period. During the switching time period, the voltage amplitude outputted by the V / F control stage is calculated by the smoothing function mathematical model. After the set switching time period, the voltage amplitude outputted by the V / F control stage is directly calculated.

[0094] The input of the smoothing function mathematical model is the voltage amplitude of the I / F control output at the switching moment, the voltage amplitude of the V / F control output at the current moment, and time.

[0095] Example 2

[0096] This embodiment provides model simulation experiment results to verify the actual effect of the V / F controlled smooth starting method and system of an electrically excited synchronous motor provided by the present invention.

[0097] A V / F control smooth start model was constructed. The motor was an electrically excited synchronous motor. The simulation was set to switch from I / F control to V / F control after reaching 150 r / min in the 4th second. The load increased from 0 to 30,000 N·m in 6.5 seconds. The target speed was set to 450 r / min, and the total simulation duration was 20 seconds.

[0098] See also Figures 6-7 As shown, Figure 6 is the motor speed simulation data,Figure 7 The motor torque simulation data is from Figures 6-7 It can be seen from the simulation results that the motor speed is relatively stable throughout the acceleration process, and there is a slight fluctuation when the control mode is switched at 4s. When the external load suddenly increases to 30000N·m at 6.5s, the motor speed fluctuates but quickly converges and continues to steadily rise to the target value. At the same time, due to the existence of the feedback loop, the system adjusts the motor current amplitude when the motor load changes, so that the electromagnetic torque quickly matches the external load.

[0099] Referring to Figure 8 , the A-phase stator current simulation data is shown in Figure 8 The simulation results show that the smooth starting method of the V / F control of the electrically excited synchronous motor can reduce the current impact during motor starting. The use of double closed-loop control increases the load damping characteristics of the system, enhances the stability and anti-slip ability of the system, and can quickly converge and stabilize in the face of speed fluctuations and load changes.

[0100] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method of smooth starting of a V / F controlled electrically excited synchronous machine, characterized in that the method The method comprises the following steps: S1, when the electrically excited synchronous motor enters an excitation stage, collecting three-phase induced electromotive force of a stator, and calculating an initial angle of a rotor through the three-phase induced electromotive force; S2, when the electrically excited synchronous motor enters an I / F control stage after a magnetic chain is established, collecting three-phase current and voltage of the electrically excited synchronous motor, feeding back to a target rotating speed through an inner ring active power control ring to adjust the rotating speed, and feeding back to a target torque current through an outer ring reactive power control ring to adjust the torque current; S3, when a running rotating speed reaches a set switching rotating speed, calculating a voltage amplitude output through a smooth function mathematical model, and entering a V / F control stage.

2. A method of smooth starting of a V / F controlled electrically excited synchronous machine according to claim 1, characterized in that, The step S1 comprises: S11, collecting three-phase induced electromotive force of a stator, and obtaining M-axis voltage observation and T-axis voltage observation in an MT rotating coordinate system after 3 / 2 conversion and coordinate conversion; S12, performing integral processing on the M-axis voltage observation to obtain a stator magnetic chain, calculating a rotating speed through the stator magnetic chain and the T-axis voltage observation, and obtaining an initial angle of a rotor by integrating the rotating speed.

3. A method of smooth starting of a V / F controlled electrically excited synchronous machine according to claim 1, characterized in that, In the step S2, the inner ring active power control ring comprises: collecting three-phase current and three-phase voltage of the electrically excited synchronous motor, obtaining current and voltage in a static two-phase coordinate system through 3 / 2 conversion, and calculating active power; feeding back a high-frequency component of the active power to the target rotating speed to adjust the rotating speed.

4. A method of smooth starting of a V / F controlled electrically excited synchronous machine according to claim 3, characterized in that, In the step S2, the outer ring reactive power control ring comprises: calculating a difference between an observed value and a true value of reactive power through current in the static two-phase coordinate system, q-axis inductance in a DQ rotor rotating coordinate system, excitation magnetic chain and the rotating speed adjusted through the inner ring active power control ring; feeding back the difference to the target torque current after PI adjustment to adjust the torque current.

5. A method of smooth starting of a V / F controlled electrically excited synchronous machine as claimed in claim 1, wherein, The step S3 comprises: setting a switching time period, calculating a voltage amplitude output in the V / F control stage through a smooth function mathematical model in the switching time period, and directly calculating the voltage amplitude output in the V / F control stage after the set switching time period; the input of the smooth function mathematical model is a voltage amplitude output at a switching time in the I / F control, a voltage amplitude output at a current time in the V / F control and time.

6. A smooth starting system for V / F control of an electrically excited synchronous machine characterized by The system comprises: a rotor initial angle identification module, configured to collect three-phase induced electromotive force of a stator when an electrically excited synchronous motor enters an excitation stage, and calculate an initial angle of a rotor through the three-phase induced electromotive force; an I / F double closed loop control module, configured to collect three-phase current and voltage of the electrically excited synchronous motor when the electrically excited synchronous motor enters an I / F control stage after a magnetic chain is established, feed back to a target rotating speed through an inner ring active power control ring to adjust the rotating speed, and feed back to a target torque current through an outer ring reactive power control ring to adjust the torque current; a V / F switching control module, configured to calculate a voltage amplitude output through a smooth function mathematical model when a running rotating speed reaches a set switching rotating speed, and enter a V / F control stage.

7. A smooth starting system for V / F control of an electrically excited synchronous machine according to claim 6, characterized in that The rotor initial angle identification module is configured to: collect three-phase induced electromotive force of a stator, and obtain M-axis voltage observation and T-axis voltage observation in an MT rotating coordinate system after 3 / 2 conversion and coordinate conversion; The M-axis voltage observation value is integrated to obtain a stator flux linkage, a rotation speed is calculated through the stator flux linkage and a T-axis voltage observation value, and the rotation speed is integrated to obtain a rotor initial angle.

8. A smooth starting system for V / F control of an electrically excited synchronous machine according to claim 7, characterized in that, The inner active power control loop comprises: Three-phase currents and three-phase voltages of the electrically excited synchronous motor are collected, the currents and the voltages in a static two-phase coordinate system are obtained through 3 / 2 conversion, and active power is calculated; A high-frequency component of the active power is fed back to a target rotation speed, so as to adjust the rotation speed.

9. A smooth starting system for V / F control of an electrically excited synchronous machine according to claim 8, characterized in that, The outer reactive power control loop comprises: A difference between an observation value and a true value of reactive power is calculated through the currents in the static two-phase coordinate system, q-axis inductance in a DQ rotor rotating coordinate system, excitation flux linkage and the rotation speed adjusted through the inner active power control loop; The difference is fed back to a target torque current after PI adjustment, so as to adjust the torque current.

10. A smooth starting system for V / F control of an electrically excited synchronous machine according to claim 6, characterized in that, The V / F switching control module is further configured to: A switching time period is set, a voltage amplitude output in a V / F control stage is calculated through a smooth function mathematical model in the switching time period, and the voltage amplitude output in the V / F control stage is directly calculated after the set switching time period; The smooth function mathematical model takes the voltage amplitude output in an I / F control stage at a switching time, the voltage amplitude output in the V / F control stage at a current time and time as inputs.

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